1. Field of the Invention
The present invention relates to aqueous polyurethane/urea dispersions containing alkoxysilane groups incorporated through secondary amino groups, to a process for preparing these dispersions and to their use for the production of coatings which have improved properties, such as solvent resistance.
2. Description of the Prior Art
The production of linear or cross-linked aqueous polyurethane-urea dispersions is known as shown by U.S. Pat. Nos. 3,479,310; 4,066,591; 4,092,286; 4,108,814; 4,237,264; and 4,238,378 which disclose linear polyurethane-ureas and U.S. Pat. Nos. 3,870,684 4,203,883 and 4,408,008, which disclose cross-linked polyurethane-ureas. The aqueous polyurethane-urea dispersions may be used for a wide range of commercial applications such as adhesives or coatings for various substrates including textile fabrics, plastic, wood, glass fibers and metals. Chemical resistance, abrasion resistance, toughness, tensile strength, elasticity and durability are among the many desirable properties of these coatings. In some cases these properties of coatings prepared from aqueous polyurethane-urea dispersions have equaled or even surpassed the performance levels of coatings obtained from solvent-based polyurethane lacquers.
Regardless of the property level which may be obtained for coatings prepared from commercial polyurethane-urea dispersions, there is always a further need to increase these properties, in particular water resistance, solvent resistance, weather resistance and physical properties such as abrasion resistance.
It is an object of the present invention to provide aqueous polyurethane/urea dispersions which can be used to prepare coatings which possess these properties and still retain the other valuable properties of aqueous polyurethane dispersions.
This object may be achieved in accordance with the present invention by preparing the aqueous polyurethane/urea dispersions which contain alkoxysilane groups incorporated through secondary amino groups.
Aqueous polyurethane dispersions containing alkoxysilane groups and known and disclosed, e.g., in U.S. Pat. Nos. 5,041,494, 5,354,808 and 5,554,686. However, in these applications the alkoxysilane groups are not incorporated through secondary amino groups as required by the present invention. An advantage of incorporating the alkoxysilane groups in accordance with the present invention is that stable dispersions can be obtained at higher siloxane group contents than when the siloxane groups are incorporated through primary amino groups.